Erosion control in a steam turbine by moisture diversion

ABSTRACT

An annular array of circumferentially spaced nozzle blades having an airfoil shaped cross section on the low pressure stages of an axial flow steam turbine wherein the stationary nozzle blades have a first slot adjacent their trailing edge and adjacent a turbine casing, a second slot adjacent the trailing edge and adjacent a rotor and a conduit connecting the slots so that water collected on the stationary nozzle blades is aspirated by the first slot, flows through the conduit, and is ejected from the second slot in atomized form and approaches the rotating blades at a location where the tangential velocity of the rotating blades is substantially lower, thus reducing the erosive effect of the water droplets on the rotating blades of the turbine.

United States Patent Heymann [4 1 Oct. 10, 1972 [54] EROSION CONTROL INA STEAM 343,407 2/1931 Great Britain ..4l5/l68 TURBINE BY MOISTUREDIVERSIQN 1,013,835 12/1965 Great Britain ..415/115 [72] Inventor: FrankJ. Heymann, Wilmington,

Del.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: March 23, 1971 [21] Appl. No.: 127,234

[52] US. Cl ..415/168, 4l5/DIG. 1 [5i] Int. Cl .Q. ..F01d l/00 [58]Field of Search ..4l5/l2l A, 168, DIG. 1,115

[56] References Cited UNITED STATES PATENTS 741,776 10/1903 Dodge..415/l2l A 1,829,674 lO/I93I Rosenlocher .4415/168 2,291,828 8/1942 New..4l5/DIG. 1 2,399,009 4/1946 Doran ..415/l21 A 3,058,720 l0/l962 Hartet a1 ..4l5/168 FOREIGN PATENTS OR APPLICATIONS 316,381 8/1929 GreatBritain .4 l5/l68 Primary Examiner-Henry F. Raduazo Attorney-A. T.Stratton, F. P. Lyle and F. Cristiano, Jr.

[57] ABSTRACT An annular array of circumferentially spaced nozzle bladeshaving an airfoil shaped cross section on the low pressure stages of anaxialtlow steam turbine wherein the stationary nozzle blades have afirst slot adjacent their trailing edge and adjacent a turbine casing, asecond slot adjacent the trailing edge and adjacent a rotor and aconduit connecting the slots so W e dwe s s .enth m eti s. biases 9esturb ne EROSION CONTROL IN A STEAM TURBINE BY MOISTURE DIVERSIONBACKGROUND OF THE INVENTION blades by steam passing thereby. Thedroplets are large and move at relatively low velocities compared to thevelocity of the tips of the rotating blades; Thus, as the large waterdroplets and rotating blades collide the impact is high resulting inerosion of the rotating blades.

Since-the leading edges of the rotating blades of the low pressurestages are the primary erosion area it has been common practice to coator form the tip of these blades of some hard material, such as Stellite;however,

providing the erosion resistant edges is expensive, is not alwaysadequate, and may weaken the blades. The rotating blades of the lowpressure stages of the turbine may also be protected by providingasuction slot adjacent the trailing edge of the nozzle blades andconnecting the slots directly to the condenser to draw the waterdirectly to the-condenser; however, this causes steam, which can douseful work, to also be extracted from the steam flow paths. Increasingthe spacing between the rotating blades and the nozzle blades willincrease the velocity of the water droplets and reduce the impactvelocity of the water droplets as they impinge on the rotating blades.However, this increases the turbine length, weight and cost.

SUMMARY OFTHE INVENTION- In general an axial flow steam turbine made inaccordance with this invention has low pressure stages operable by steamhaving water droplets therein and has a rotor, a plurality of annulararrays of circumferentially spaced rotatable blades fastened to therotor, a casing encirclingthe arrays of rotatable blades and the rotor,and an annular array of circumferentially spaced stationary nozzlebladesfastened to the casing for directing steam against the rotatable blades.The stationary nozzle blades of at least one array of stationary nozzleblades each comprise a leading edge and a trailing edge, the trailingedge being adjacent the rotatable blades against which it directs steam,a first port adjacent the trailing edge and adjacent the casing, asecond portadjacent the rotor, and a conduit connecting the ports. Theports and conduits are so disposed that water droplets collected on thenozzle blade are aspirated therefrom by the first port, flow through theconduit and are ejected from the second port in atomized form andapproach the rotatable blades at a greater velocity than water dropletswhich are swept off the trailing edge of the nozzle blade by steamflowing thereby and at a location where the tangential velocity of therotating blade is substantially lower, thus reducing the erosive effectof the water droplets on the adjacent array of rotatable blades againstwhich the nozzle blades direct steam.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of thisinvention will become more apparent from reading the following detaileddescription in connection with the accompanying drawings, in which:

FIG. 1 is a partial sectional view of the low pressure stages of anaxial flow steam turbine;

FIG. 2 is an enlarged partial sectional view of a stationary nozzleblade and a rotatable blade made in accordance with this invention;

FIG. 3 is an enlarged partial sectional view of a stationary nozzleblade and an associated rotatable blade with a superimposed velocitydiagram showing the velocity of the steam and the water droplets as thedroplets are swept off the nozzle blade by the steam;

FIG. 4 is an enlarged partial sectional view of a stationary nozzleblade and an associated rotatable blade with a superimposed velocitydiagram showing the velocities of the steam and atomized water dropletsas the droplets approach the rotatable blade;

FIG. 5 is an enlarged partial sectional view of a stationary nozzleblade showing the disposition of the second port in a concave portionofthe stationary nozzle blade;

FIG. 6 is an enlarged partial sectional view of a stationary nozzleblade showing the disposition of the second port in a convex portion ofthe stationary nozzle blade;

FIG. 7 is an enlarged partial sectional view of a stationary nozzleblade showing the second port disposed in a shroud ring, and

FIG. 8 is an enlarged partial sectional view of a stationary nozzleblade and a rotatable blade wherein the nozzle blade is tapered adjacentthe rotor.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawing in detail, FIG. 1 shows the low pressure stage of an axial flowsteam turbine 1 having a rotor 3, a plurality of annular arrays ofcircumferentially spaced rotatable blades 5 fastened to the rotor 3, acasing 7 encircling the rotatable blades 5 and the rotor3, and anannular array of circumferentially spaced stationary nozzle blades 9interposed between two annular arrays of rotatable blades 5 and fastenedto the casing 7 by an internal cylinder 11.

As shown in FIG. 1, the stationarynozzle blades 9 of the annular arrayof nozzle blades are fastened together adjacent the rotor 3 by a shroudring 12 subtending the annular array of stationary nozzle blades. Thenozzle blades 9 have a rounded leading edge 13 adjacent the upstreamside thereof, the right edge as shown in the drawings, a relativelysharp trailing edge 15, the

downstream edge or left edge as shown in the drawings, and an airfoilshaped cross section. The airfoil shaped cross section is curved tochange the direction of the motive steam as it passes through thestationary nozzle blades; thus each nozzle blade has a concave andconvex surface or portion 16 and 17, respectively.

As shown in FIG. 2, a first port 19 is disposed adjacent the trailingedge 15 of the nozzle blade 9 and adjacent the casing end or root 21 ofthe nozzle blade 9. The first port 19 is shown in FIG. 2 to be a slotextending lengthwise of the nozzle blade.

A second port 23 is disposed on or adjacent the trailing edge 15 of thenozzle blade 9 and radially inwardly respect to the first port 19 oradjacent the rotor end 25 of the nozzle blade 9. A conduit 27 connectsthe ports 19 and 23 so that water droplets collected on the nozzle blade9 are aspirated therefrom by the first port 19, flow through the conduit27, are ejected from the second port 23 and approach the rotatableblades at a greater velocity than water droplets, which would be sweptoff the trailing edge 15 of the nozzle blades by steam flowing therebyif the ports 19 and 23 were not so disposed, thus reducing the erosiveeffect of the water droplets on the rotatable blade.

The reduction in erosion of the rotating blades caused by waterimpinging thereon is a result of increasing the velocity of the waterdroplets decreasing the mass of the droplets and causing the waterdroplets to impinge on the blades adjacent the rotor, where the rotatingblade velocity is at a minimum, rather than adjacent the blade tips,where the rotating blade velocity is at a maximum. This may be betterunderstood by referring to the vector diagrams in FIGS. 3 and 4. Thevector diagram in FIG. 3 shows the steam velocity CA as it leaves thenozzle blades 9; the velocity of the water droplets CA being swept offthe trailing edge 15 of the nozzle blade 9 by the steam, when the nozzleblades are not made in accordance with this invention, the velocity ofthe rotating blades AB; the velocity of the steam relative to therotating blades OB; and the velocity of the water droplets relating tothe rotating blades CB. The absolute velocity of the water dropletsrelative to the rotating blades is only slightly less than the absolutevelocity of the rotating blades, but, as noted in the velocity diagram,is in the opposite direction. Thus, the water droplets will collide withthe rotating blades at a velocity close to the velocity of the rotatingblades and the impact of the water droplets on the rotating bladescauses erosion adjacent to the leading edge of the rotating blades. Thevector diagram of FIG. 4 shows the steam velocity O'A' as it leaves thenozzle blade 9; the velocity of the atomized water droplet C'A' as thedroplets approach the rotating blade; the velocity of the rotatingblades A'B'; the velocity of the steam relative to the rotating blades0'8; and the velocity of the atomized water droplets relative to therotating blades C'B', which is the velocity at which the water dropletscollide with the rotating blades. It should be noted that the absolutevalue of the velocity of the water droplets relative to the rotatingblade CE is substantially less than the absolute value of the velocityCB. This is mainly due to the fact that the velocity of the rotatingblade is lower adjacent the rotor and in part due to the fact that thevelocity of the atomized water droplets is greater as they approach therotating blades.

The differential static pressure has a ratio of approximately 2:1between the area adjacent the casing and the area adjacent the rotor.The higher pressure adjacent the casing or tip region of the rotatingblades is created by the centrifugal compression of the steam as therotatable blades revolve. The rotation of the rotatable blades alsocauses the water droplets to sling outwardly toward the casing, thus themajority of the moisture in the steam will collect on the stationaryblades adjacent the casing. With the pressure of the steam adjacent therotor about one-half the pressure of the steam adjacent the casing,there is sufficient pressure differential to cause water dropletsaspirated by the first port to flow to the second port so that byproviding a small aperture at the second port the water droplets willbreak up into small atomized droplets. Since the atomized droplets haveless mass, their acceleration by the steam is greater and their absolutevelocity as they approach the rotating blades is greater, thus theirimpact velocity is less, and the impact and erosion effect on rotatingblades is reduced considerably, for the erosion varies generally as thefifth power of the impact velocity.

To further increase the velocity of the water droplets, the second port23 may be disposed in the convex portion of the nozzle blade 9 adjacentthe rotor 3. At this location the pressure of the steam is at itsminimum, thus the pressure differential between the first and secondport 19 and 23, respectively, is at its maximum; however, the boundarylayer is thick and sensitive to disturbance. Therefore, to increase thepressure differential to its maximum and provide good atomization, aprotrusion or knob 29 is disposed on the convex surface 16 of the nozzleblade 9 adjacent the I rotor 3. The second port 23 is disposed in theprotrusion 29, as shown in FIG. 6. The protrusion 29 projects beyond theboundary layer to provide the optimum pressure differential between thetwo ports.

The second port 23 may also be disposed in the concave portion 16 of thenozzle blade 9, as shown in FIG. 5. While the boundary layer is thinnerand less sensitive to disturbance the static pressure is slightly higheradjacent this portion of the nozzle blade, thus reducing the pressuredifferential between the two ports.

FIG. 8 shows the trailing edge 15 of the nozzle blade 9 adjacent therotor 3 tapered inwardly away from the rotating blade 5 against which itdirects steam. The second port is disposed in the tapered portion of thenozzle blades to increase the distance the atomized water dropletstravel with the steam causing an increase in their velocity and areduction in the impingement velocity of the droplets on the rotatingblades.

As shown in FIG. 7 the second port 23 is disposed in the shroud ring 12and can be so disposed as to admit the water droplets at any distancefrom the rotating blades to optimize the atomization of the droplets andtheir velocity.

Atomizing the water droplets decreases their mass, provides them with aninitial velocity as they leave the second port and allows them toaccelerate rapidly in the steam flow stream so that as they approach therotating blades adjacent the rotor, where the velocity of the rotatingblade is at its minimum, the water droplets impingement velocity on therotating blades is minimized, thus reducing the erosive effect of thewater droplets on the rotating blades.

What is claimed is:

1. An axial flow steam turbine having low pressure stages operable bymotive steam having water droplets therein, the turbine having a rotor,a plurality of annular arrays of circumferentially spaced rotatableblades fastened to said rotor, a casing encircling said array ofrotatable blades and said rotor, and a plurality of annular arrays ofcircumferentially spaced stationary nozzle blades fastened to saidcasing for directing steam against said blades, said nozzle blades of atleast one array of stationary nozzle blades comprising a leading edgeand a trailing edge, said trailing edge being adjacent said rotatableblades against which it directs steam,

a first port adjacent said trailing edge and adjacent said casing,

a second port adjacent said rotor and spaced radially inwardly of thefirst port and so disposed to be in communication with the motive steamat a lower pressure than the first port, and

a conduit connecting said ports,

said ports and conduits being so disposed that water droplets collectedon said nozzle blade are aspirated therefrom by the first port, flowthrough said conduit, and are ejected from said second port in atomizedform and at a greater velocity than water droplets being swept off thetrailing edge of said nozzle blade by steam flowing thereby, thusreducing the erosive effect of the water droplets on said rotatableblades.

2. An axial flow steam turbine as set forth in claim 1', wherein thefirst port is a slot extending lengthwise of the nozzle blade.

3. A turbine as set forth in claim 1, wherein the nozzle blades of theone array of nozzle blades have a rounded leading edge, a relativelysharp trailing edge, and an airfoil shaped cross section, which iscurved to change the direction of the steam flowing through the nozzleblades, the second port being disposed in the concave portion of thenozzle blade.

4. An axial flow steam turbine as set forth in claim 1, wherein thenozzle blades of one array of nozzle blades have a rounded leading edge,a relatively sharp edge and an airfoil shaped cross section which iscurved to change the direction of the steam flowing thereby, the secondport being disposed in the convex portion of the nozzle blade.

5. A turbine as set forth in claim 4, wherein the nozzle blades of theone array of stationary nozzle blades have a protrusion disposed in theconvex portion thereof adjacent the rotor and the second port isdisposed in said protrusion.

6. A turbine as set forth in claim 4, wherein the nozzle blades of theone array of stationary nozzle blades have a protrusion disposed in theconvex portion thereof adjacent the rotor, said protrusion extendingbeyond a boundary layer of steam flowing thereby and the second portbeing disposed in said protrusion.

7. An axial flow steam turbine as set forth in claim 1, furthercomprising an inner shroud ring fastened to the array of stationarynozzle blades adjacent the rotor, the second port being disposed in saidshroud ring.

8. A turbine as set forth in claim 1, wherein the nozzle blades of theone array of stationary nozzle blades are tapered adjacent the rotor toincrease axial spacing between the nozzle blades and the rotatableblades, the second port being disposed in said tapered portion of thenozzle blades.

1. An axial flow steam turbine having low pressure stages operable bymotive steam having water droplets therein, the turbine having a rotor,a plurality of annular arrays of circumferentially spaced rotatableblades fastened to said rotor, a casing encircling said array ofrotatable blades and said rotor, and a plurality of annular arrays ofcircumferentially spaced stationary nozzle blades fastened to saidcasing for directing steam against said blades, said nozzle blades of atleast one array of stationary nozzle blades comprising a leading edgeand a trailing edge, said trailing edge being adjacent said rotatableblades against which it directs steam, a first port adjacent saidtrailing edge and adjacent said casing, a second port adjacent saidrotor and spaced radially inwardly of the first port and so disposed tobe in communication with the motive steam at a lower pressure than thefirst port, and a conduit connecting said ports, said ports and conduitsbeing so disposed that water droplets collected on said nozzle blade areaspirated therefrom by the first port, flow through said conduit, andare ejected from said second port in atomized form and at a greatervelocity than water droplets being swept off the trailing edge of saidnozzle blade by steam flowing thereby, thus reducing the erosive effectof the water droplets on said rotatable blades.
 2. An axial flow steamturbine as set forth in claim 1, wherein the first port is a slotextending lengthwise of the nozzle blade.
 3. A turbine as set forth inclaim 1, wherein the nozzle blades of the one array of nozzle bladeshave a rounded leading edge, a relaTively sharp trailing edge, and anairfoil shaped cross section, which is curved to change the direction ofthe steam flowing through the nozzle blades, the second port beingdisposed in the concave portion of the nozzle blade.
 4. An axial flowsteam turbine as set forth in claim 1, wherein the nozzle blades of onearray of nozzle blades have a rounded leading edge, a relatively sharpedge and an airfoil shaped cross section which is curved to change thedirection of the steam flowing thereby, the second port being disposedin the convex portion of the nozzle blade.
 5. A turbine as set forth inclaim 4, wherein the nozzle blades of the one array of stationary nozzleblades have a protrusion disposed in the convex portion thereof adjacentthe rotor and the second port is disposed in said protrusion.
 6. Aturbine as set forth in claim 4, wherein the nozzle blades of the onearray of stationary nozzle blades have a protrusion disposed in theconvex portion thereof adjacent the rotor, said protrusion extendingbeyond a boundary layer of steam flowing thereby and the second portbeing disposed in said protrusion.
 7. An axial flow steam turbine as setforth in claim 1, further comprising an inner shroud ring fastened tothe array of stationary nozzle blades adjacent the rotor, the secondport being disposed in said shroud ring.
 8. A turbine as set forth inclaim 1, wherein the nozzle blades of the one array of stationary nozzleblades are tapered adjacent the rotor to increase axial spacing betweenthe nozzle blades and the rotatable blades, the second port beingdisposed in said tapered portion of the nozzle blades.